RP - Osmosis

  • Created by: India.02
  • Created on: 11-05-19 18:52
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  • RP - Osmosis
    • Method
      • 1. Cut a potato into identical cylinders and get some beakers with different sugar solutions - one should be pure water and the other should be very concentrated sugar solution
      • 2. Measure the mass of the cylinders and leave one cylinder in each beaker for 24 hours
        • 3. Remove the cylinders - dry with a paper towel - measure the masses again
      • 4. If the cylinders have drawn in mass by osmosis - increased mass - if water has been drawn out - decreased mass
        • Calculate the % change in mass and then plot a few graphs to compare
      • Dependant variable - mass of the potato - Independent variable - concentration of sugar solution
        • All other variables - volume, time, sugar type, temp - must be kept the same for a fair test
      • Errors - potato wasn't fully dried, the excess water would increase the mass - if water evaporated from beakers, concentration of solution would change
        • Reduce effect by repeating the experiment and calculating a mean %change at each concentration
    • Osmosis
      • Movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of low water concentration
      • Partially permeable membrane has very small holes in it - only tiny molecules (water) can pass - big molecules (sucrose) can't
      • Water molecules pass both ways through the membrane because water molecules move about randomly all the time
      • As there are more water molecules on one side, there is a steady net flow of water into the region with fewer water molecules - into the stronger sugar solution
      • The strong sugar solution becomes more dilute - the water tries to balance the concentration on each side of the membrane
      • Osmosis - type of diffusion - passive movement of water particles from an area of high concentration to an area of low concentration

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